Listener rules and routing in AWS - Mini Project: Build & Apply

Listener Rules and Routing in AWS Application Load Balancer

📖 Scenario: You are setting up an AWS Application Load Balancer (ALB) to route incoming web traffic to different target groups based on URL paths. This helps your website serve different content or services efficiently.

🎯 Goal: Build an AWS ALB listener configuration with rules that route requests to specific target groups based on URL path patterns.

📋 What You'll Learn

Create a listener on port 80 for the ALB

Define two target groups: tg-api and tg-web

Add listener rules to route requests with path /api/* to tg-api

Add listener rules to route requests with path /web/* to tg-web

Add a default action to forward requests to tg-web

💡 Why This Matters

🌍 Real World

Routing web traffic to different backend services based on URL paths is common in microservices and multi-tenant web applications.

💼 Career

Understanding ALB listener rules and routing is essential for cloud engineers and DevOps professionals managing scalable web infrastructure.

1

Create Target Groups

Create two target groups named tg-api and tg-web with protocol HTTP and port 80.

AWS

# Create target group tg-api
# Create target group tg-web

Need a hint?

Use aws_lb_target_group resource with name, port, protocol, and vpc_id.

2

Create ALB Listener on Port 80

Create an ALB listener resource named alb_listener that listens on port 80 for protocol HTTP and uses the ALB ARN aws_lb.main.arn.

AWS

resource "aws_lb_target_group" "tg_api" {
  name     = "tg-api"
  port     = 80
  protocol = "HTTP"
  vpc_id   = "vpc-12345678"
}

resource "aws_lb_target_group" "tg_web" {
  name     = "tg-web"
  port     = 80
  protocol = "HTTP"
  vpc_id   = "vpc-12345678"
}

# Create ALB listener on port 80

Need a hint?

Use aws_lb_listener resource with load_balancer_arn, port, protocol, and default_action.

3

Add Listener Rule for /api/* Path

Add a listener rule resource named api_rule that matches requests with path pattern /api/* and forwards them to the target group tg-api. Use aws_lb_listener.alb_listener.arn as the listener ARN and set the rule priority to 10.

AWS

resource "aws_lb_target_group" "tg_api" {
  name     = "tg-api"
  port     = 80
  protocol = "HTTP"
  vpc_id   = "vpc-12345678"
}

resource "aws_lb_target_group" "tg_web" {
  name     = "tg-web"
  port     = 80
  protocol = "HTTP"
  vpc_id   = "vpc-12345678"
}

resource "aws_lb_listener" "alb_listener" {
  load_balancer_arn = aws_lb.main.arn
  port              = 80
  protocol          = "HTTP"
  default_action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.tg_web.arn
  }
}

# Add listener rule for /api/* path

Need a hint?

Use aws_lb_listener_rule with listener_arn, priority, action, and condition for path pattern.

4

Add Listener Rule for /web/* Path

Add a listener rule resource named web_rule that matches requests with path pattern /web/* and forwards them to the target group tg-web. Use aws_lb_listener.alb_listener.arn as the listener ARN and set the rule priority to 20.

AWS

resource "aws_lb_target_group" "tg_api" {
  name     = "tg-api"
  port     = 80
  protocol = "HTTP"
  vpc_id   = "vpc-12345678"
}

resource "aws_lb_target_group" "tg_web" {
  name     = "tg-web"
  port     = 80
  protocol = "HTTP"
  vpc_id   = "vpc-12345678"
}

resource "aws_lb_listener" "alb_listener" {
  load_balancer_arn = aws_lb.main.arn
  port              = 80
  protocol          = "HTTP"
  default_action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.tg_web.arn
  }
}

resource "aws_lb_listener_rule" "api_rule" {
  listener_arn = aws_lb_listener.alb_listener.arn
  priority     = 10
  action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.tg_api.arn
  }
  condition {
    path_pattern {
      values = ["/api/*"]
    }
  }
}

# Add listener rule for /web/* path

Need a hint?

Use aws_lb_listener_rule with listener_arn, priority, action, and condition for path pattern.